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Oct. 1, 1929. s l 1,729,803

AUTOMATIC TELEPHONE SYSTEM Filed Oct. 17, 1924 2 Sheets-Sheet, 1

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AUTOMATIC TELEPHONE SYSTEM Filed Oct. 17, 1924 2 Sheets-Sheet 2 -Inusn2ur Patented Oct. 1, 1929 UNITE STATS PATENT orrlce RUDOLPH F. STEI-ILIK, OF CHICAGO, ILLINOIS, ASSIGNOB, BY MESNE ASSIGNMENTS,

TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE AUTOMATIC TELEPHONE SYSTEM Application filed October 17, 1924. Serial No. 744,119.

The present invention relates in general to automatic telephone systems, but is concerned more particularly with improved circuit arrangements for the automatic switches that are employed in telephone systems; and the principal object is the production of new and improved circuit arrangements whereby automatic switches may operate more satisfactorily under severe conditions, including those imposed by exceedingly heavy traffic, and also those imposed by calling lines having adverse characteristics as regards their use in controlling automatic switches.

This case may be considered an improvement on my Patents, No. 1,621,791, May 29, 1928, and No. 1,693,124, Nov. 27, 1928, and, when considered in the light of these applications, one specific feature of the present invention is the production of an improved circuit arrangement whereby the switchingthrough operation of a selector switch is rendered less critical in that it does not depend upon so great a nicety of adjustment of the various relays concerned, as will be herein- *1 after pointed out.

Another object has to do with a new and improved arrangement for making a selector switch or a connector switch busy during the time it is being restored to its normal position after it has been in use. Applicant is aware of the fact that this result is not broadly new. However, the arrangement for ac complishing this result in the present case 111-- volves two distinct pointsof novelty. In the first place, the usual slow acting change-over relay is again brought into play upon the release of the switch to bring about the ground ing of the release trunk to hold the switch busy, and in the second place the grounding of the release trunk conductor, in the case of E of the series relay and before the ground potential is reapplied to the release trunk conductor. The time required for these two relays to pull up, one after the other, added to the time previously required for the associated switching relay to fall back, is long enough to insure that the ground potential is not reapplied to the release trunk conductor before the switching relay (or relays, as the case may be) of the switch or switches preceding the one in question has had time to fall back.

According to another feature of the invention, the circuits of the connector switch have been re-arranged so that the same slow acting change-over relay is used during both the vertical and the rotary movements. This permits the circuits ordinarily involved in shifting the impulse conductor from the vertical magnet to the rotary magnet to be greatly simplified, and further simplifies the adjustments and the maintenance of the adjustments of the connector switches because now only one slow acting change-over relay is operated from a given connector line relay as against two in the ordinary type of connector.

Other features, not specifically mentioned now, but having to do mainly with the various circuit details involved in carrying out the above objects, will become apparent upon further perusal of the specification in connection with the accompanying drawings comprising Figs. 1 1:, inclusive.

Referring now to the accompanying drawings, which show by means of the usual circuit diagrams a suflicient amount of apparatus in a telephone system embodying the fea tures of the invention to enable the same to be understood, Figs. 1 and 2, taken together, showthe apparatus involved in a single connection between the line of substation A and the line of substation B, and Figs. 3 and 4 show desirable modifications of the selector switch shown in Fig. 1.

The substations A and B are of the usual automatic type, and the associated lines terminate, respectively, in the line switches LS and LS at the exchange.

The line switch LS is mechanically of the usual rotary type in which the wipers have no normal position and are moved in a forward direction only. The line switch LS is similar to the line switch LS.

The selector S, mechanically, is a vertical and rotary switch having bank contacts arranged in horizontal rows or levels, the wipers being brought opposite a desired level of contacts by the vertical movement, and being brought into engagement with a particular contact in the selected level by the rotary movement. The selector S, as well as the connector C, is similar mechanically to the selector S. I

In the drawings, the relays which are slow acting have been indicated in different ways, according to the method used in making them slow acting. The relays, such as relay 6 of the line switch LS, Fig. 1, which have copper slugs on the armature end-of their cores, are indicated by making the upper portion of the core solid black. Such relays are slow to pull up in addition to being slow to fall back. The relayswhich have copper sleeves around the entire length or their cores are indicated in the conventional manner by a couple of extra lines, such for example as relay 23 of the selector S, Fig. 1. Such relays are slow to fall back, but are not noticeably slow to pull up. It will be noted that the ring cutoff relay 105 of the connector C, Fig. 2, has both a copper sleeve and a copper collar on its armature end. These two combine in lowering the impedance of the relay to ringing current, and the action of the copper collar on the armature end of the relay prevents the relay from operating in response to the alternating ringing current.

The apparatus having been described generally, a detailed description of the operation of the apparatus involved in extending a connection from the line of substation A to the line of substation B will now be given.

Vhen the subscriber at substation A, de-

, siring to converse with the subscriber at substation E, removes his receiver, a circuit is closed over line conductors 2 and 3 for line relay 6 of the line switch LS. Line relay 6 thereupon energizes and places ground upon the private normal conductor 4 at armature 10, thereby making the calling line busy to the connector switches having access to it and closing a circuit for switching relay 5 and stepping magnet 12 in'series. Line relay 6 also at armature 11 connects test wiper 14 to the junction of relay 5 and magnet 12. Accordingly, the further operation depends upon whether or not the trunk line upon which the Wipers of the line switch are standing is busy or idle. If thistrunk line is idle, the connecting up of the test wiper 14 atarmature 11 does not have any particular effect and switching relay 5 energizes, seizing the trunk.

Assuming, on the other hand, that the trunk line in question is busy, test wiper 14 engages a grounded test contact and switch ing relay 5 is short'circuited and does not energize, and stepping magnet 12, which interrupts its own circuit, operates in a buzzer-like manner, advancing the wipers 1315, inclusive, in search of an idle trunk.

lVhen an idle trunk is reached, which trunk it will be assumed is the one comprising conductors 1618, inclusive, switching relay 5, being no longer short circuited, energizes in series with stepping magnet 12, but stepping magnet 12 does not energize at this time on account of the relatively high resistance of switching relay 5. Upon energizing, switching relay 5 opens the test circuit and prepares the holding circuit at armature 8; and at armatures 7 and 9 disconnects the line conductors 2 and 3 from line relay 6 and ground, respectively, and extends them by way'of wipers 13 and 15, conductors 16 and 18', and armatures 38 and 41 to the windings of line relay 21 of the selector S. Lin-e relay 21 now energizes and closes at armature 32 a circuit for release relay 22 which includes the resting contact and armature 37 and rotary magnet 29. Release relay 22 energizes over this circuit but rotary magnet 29 does not energize on account of the relatively high resistance of release relay 22. It will be noted that during the time the normally closed contacts controlled by armature 32 are closed after armature 32 comes into engagementwith its working contact and before said normally closed contact opens, the low wound series relay 23 is in multiple with release relay 22 and in the circuit of rotary magnet 29. How ever, rotary magnet 29 is not operated from this source, owing to the exceedingly short time during which this circuit remains closed. Upon energizing, relay 22 opens a point in the circuit of release magnet 27 and prepares a circuit for vertical magnet 26 at armature 34, thereby closing a locking circuit for itself which includes vertical magnet 26, working contact and armature 34, and the resting contact and armature 40. This circuit is effective in maintaining the release relay 22 energized after the initial circuit through rotary magnet 29 is opened, as will be subsequently pointed out. As a further result of the energization of release relay 22', it places ground upon release trunk conductor 17 at armature 33, thereby closing a circuit through test wiper 14 and armature 8 and its working contact, for switching relay 5 of the line switch LS before the slow acting line relay 6 has had time to deenergize and open the initial circuit of switching relay 5 at armature 10. p

The above operations have taken place, as previously mentioned, responsive to the re moval of the receiver at substation A, and the circuits are now in condition for the first digit in the desired number to be dialled. Accord ingly, when the calling subscriber manipu lates his calling device in accordance with the first digit in the desired number, line relay 21 deenergizes a corresponding number of times and, upon each deenergization, replaces the low wound series relay 23 in multiple with release relay 22, thereby practically short circuiting the latter. Accordingly, upon each deenergization of line relay 21, vertical mag net 26 is energized in series with series relay 23 and it deenergizes again upon the subsequent energization of line relay 21 when relay 23 is disconnected from in multiple with relay 22. Although relay 22 is shunted by series relay 23, upon each momentary deenergization of line relay 21 to such an extent that it would eventually deenergize, it does not fall back at this time because of the slow acting effect of its shunted winding.

By the operation of vertical magnet 26, the wipers 4244, inclusive, of the selector S are raised step by step and come to rest opposite the desired level of bank contacts. Relay 23 is energizes in series with vertical magnet 26 and, being slow acting due to the presence of the copper sleeve around its core and also due to the fact that it is shunted by the associated resistance winding, maintains its armature attracted throughout the vertical movement. Upon energizing, relay 23 disconnects private wiper 43 at armature and connects the latter to ground, at the same time opening a point in the operating circuit of rotary magnet 29 which is to be closed subsequently. Connecting armature 35 to ground prepares a circuit for stepping relay 24. Accordingly, upon the closure of the oil normal contacts 31, which occurs upon the first vertical step, stepping relay 24 energizes in series with interrupter contacts 30 and armature 35 and its working contact and locks itself to the grounded release trunk conductor 17 at armature 36, at the same time disconnecting rotary magnet 29 from armature 32 of line relay 21 at armature 37 and preparing a circuit for rotary magnet 29 through the normally closed contacts controlled by armature 35.

It will be appreciated, of course, that the energization of stepping relay 24 occurs during the transmission of the first impulse oi" current to vertical magnet 26 through series relay 23, and that rotary magnet 29 is accordingly disconnected from armature 32 before line relay 21 subsequently energizes to disconnect series relay 23 from in. multiple with release relay 22 and thereby bring about the first deenergization of vertlcal magnet 26. The reason for disconnectmg rotary magnet I 29 from armature 32 at this time is to prevent rotary magnet 29 from being connected in multiple with vertical magnet 26 at the time the operating circuit of the latter through series relay 23 is opened, as this would result in provision of a discharge path through rotary magnet 29 for the momentary high potential induced by the winding of vertical magnet 26 at the time of the opening of its energizing circuit, which would, of course,

have a tendency to make vertical magnet 26 slow to deenergize. Furthermore, the disconnecting of armature 32 at armature 37 upon the energization of stepping relay 24 prevents the reverse action between the vertical and rotary magnets during the rotary movement, as will be pointed out subsequently.

At the end of the transmission of the first digit, line relay 21 comes to rest in an energized condition and vertical magnet 26 remains deenergized. Shortly thereafter, the slow acting series relay 23 falls back and completes the circuit of rotary magnet 29 at the normally closed contacts controlled by armature 35. Rotary magnet 29 thereupon energizes and advances the wipers 42-44, inclusive, into engagement with the first set of bank contacts in the selected level, and, near the end of its stroke, opens at the interrupter contacts 30 the circuit of stepping relay 24. Stepping relay 24 accordingly cleenergizes and opens the circuit of rotary magnet 29 at armature 37 and connects rotary magnet 29 to armature 32 of line relay 21 again. This latter operation has no particular utility at this time and merely incidental. it will be seen that no ill effect accompanies the connection of rotary magnet 29 to armature 32 and consequently to vertical magnet 26 on account of the fact that the contacts associated with armature 37 are not of the malre-before-break variety and accordingly the first high potential induced by the breakin g of the-circuit of rotary magnet 29 has time to subside before the rotary magnet is connected in multiple with vertical magnet 26. Rotary magnet 29 is therefore not made slow acting by this arrangement.

Rotary magnet 29 deenergizes responsive to the opening of this circuit at armature 37 of relay 24 and again closes its interrupter contacts 30. From this point, the further operation depends upon whether the trunk line terminating in the first set of bank contacts is busy or idle. If it is idle, test wiper 43 does not encounter a ground potential and switching relay 25 energizes immediately, seizing the trunk.

Assuming, on the other hand, that the first trunk engaged by the wipers of the selector S is busy, test wiper 43 encounters a grounded bank contact and switching relay 25 is short circuited and does not energize at this time. Also, the ground potential encountered by test wiper 43 energizes stepping relay 24 which again closes its locking circuit at armature 36 and at armature 37 again closes the circuit of rotary magnet 29. Rotary magnet 29 now energizes again and the wipers are advanced to the next set of bank contacts.

This alternate operation of stepping relay 24 and rotary magnet 29 continues as described until a set of bank contacts associated with an idle trunk is reached, which trunk, it will be assumed, is the one comprising conductors -47, inclusive. When this trunk is reached, switching relay 25, being no longer short circuited, energizes in series with stepping relay 24 upon the closure of interrupter contacts when rotary magnet 29 falls back after having stepped the wipers to the idle trunk. Stepping relay 24, however, is not energized at this time owing to the high resistance of switching relay 25. Upon energizing, switching relay 25 disconnects vertical magnet 26 at armature 40, so as to prevent a false operation of vertical magnet 26 upon the deenergization of line relay 21 which is to follow and also so as to prevent the premature energization of release magnet 27 upon the deenergization of release relay 22, which is to follow. Release relay 22 does not de energize responsive to the disconnection of vertical magnet 26, because it is now maintained energized again over its initial circuit which includes rotary magnet 29. As a further result of the energization of switching relay 25, it disconnects test wiper 43 from the junction of stepping relay 24 and switching relay 25 and connects it to the grounded release trunk conductor 17, thereby making the seized trunk busy immediately and preparing the usual holding circuit for the selector S and the line switch LS; and at armatures 38 and 41 relay 25 disconnects conductors 16 and 18 fromline relay 21 and extends them by way of wipers 42 and 44, the bank contacts with which these wipers are in engagement, conductors 45 and 47, and thenormally closed contacts controlled by armatures 122 and 123 to line relay 102 of the connector C. Line relayv 102 now energizes over the calling line and closes at armature 125 a circuit for release relay 103 through vertical magnet 111. Release relay 103 accordingly energizes, but vertical magnet 111 does not energize on account of the high resistance of relay 103. Upon energizing, relay 103 places ground on the local locking conductor 115 at armature 126; opens a point in the circuit of release magnet 109 and prepares an operating circuit for vertical magnet 111 at armature 128; and at armature 127 places ground upon release trunk conductor 46, thereby closing the usual holding circuit for the switching relays of the selector S and the line switch LS before the release relay 22 deenergizes. It may be pointed out that the deenergization of release relay 22 is brought about responsive to the deenergization of line relay 21 when it is dis connected by switching relay 25. Relay 21 first shunts relay 22 with the low wound series relay 23 at the normally closed contacts controlled by armature 32 and then disconnects rotary magnet 29 from the circuit of the two relays at armature 32. Relay 22 is slow to deenergize responsive to the opening of its energizing circuit at this time, because it is practically short circuited by the low Wound series relay 23.

The calling subscriber may now dial the second digit in the desired number and, when he does so, line relay 102 of the connector C is deenergized a corresponding number of times and, upon each deenergiza-tion, connects the low wound series relay 107 in multiple with relay 103 at the normally closed contacts controlled by armature 125. Vhen this occurs, vertical magnet 111 energizes in series a with relay 107 through the normally closed contacts controlled by armature 130, worklng' contact and armature 128 and the normally closed contacts controlled by armature 125. Release relay 103, although practically short circuited by relay 107, does not deenergize during the series of closures of the operating circuit of? vertical magnet 111101 the same reason pointed out in connection with release relay ot the selector S. By the operation oi vertical magnet 111, the wipers 146148 are raised step by step and come to rest opposite the desired level of bank contacts. Relay 107 is energized in series with vertical magnet 111 and, being slow actin its armature attracted throughout the vertitil movement, thereby maintaining the circuit of relay 104 open at armature 139 after oil normal contacts 113 have closed, as they do upon the first vertical step.

At the end of the vertical movement, relay 107 deenergizes, completing at armature 139 a circuit from ground by way of armature 142 of relay 10S and its resting contact,

through armature 139 and its resting contact,

03' normal contacts 113, and the normally closed contacts controlled by armature 129 for relay 104. Relay 104 thereupon energizes and connects rotary magnet 112 to the operating circuit at armature 130, at the same time disconnecting vertical magnet 111, and at arniiature 12S) relay 104 closes a locking circuit for itself to the grounded release trunk c0nductor 46, at the same time opening its initial circuit.

The calling subscriber may now dial the third and last digit in the desired number and, when he does so, line relay 102 deener' gizes a corresponding number of times and, upon each deencrgization, operates rotary magnet 112 in the manner described above in connection with vertical magnet 111. By the operation of rotary magnet 112, the wipers 146 -14 8, are rotated step by step and come into engagement with the set of bank contacts in which the line of substation B terminates. Relay 107 is energized in series with rotary magnet 112 and at armature 138 disconnects test wiper 147 from the upper or test winding oi switching relay 107 and connects it instead to busy relay 106 through the resting contact and arn'iature 143. Accordingly, busy relay 106 i free to energize and deenergize under the control of test wiper 147 as it rotates across the various test contacts on its way to the test contact of the called line, but busy maintains relay 106 cannot lock itself energized at this time, owing to the fact that a point in its looking circuit is held open at the normallyclosed contacts controlled by armature 138 of series relay 107.

The further operation after the wipers come to rest upon the bank contacts of the called line, depends upon whether or not the called line is idle. In case the called line is busy at this time, busy relay 106 is energized and a self-locking circuit is prepared at armature 135. Accordingly, When series relay 107 falls back shortly after the termination of the last rotary impulse, busy relay 106 is locked energized from ground on the grounded release trunk conductor 46 through armature 135 and its working contact, normally closed contacts controlled by armature 138, and the resting contact and armature 143. It will be noted that the grounded release trunk conductor is maintained disconnected from the upper winding of switching relay 108 at the resting contact of armature 135, so that switching relay 108 cannot energize in case the called line subsequently becomes idle. Furthermore, busy relay 106 at armature 1.36 places a shunt around series relay 107 so that in case the calling subscriber again manipulates his calling device and operates rotary magnet 112 to bring the wipers into engagement with a new line, relay 107 does not operate and busy relay 106 remains energized. It will be noted that the circuit for shunting relay 107 includes armature 142 of relay 108 and its resting contact, and armature 139 and its resting contact, and, since this circuit includes armature 139 and its resting contact, it is not completed by the energizations of vbusy relay 106 during the initial rotary movement of the connector because of the fact that series relay 107 is energized at that time and maintains the shunting circuit open at armature 139. As a further result of the energization of busy relay 106, it connects the busy tone lead 114 at armature 137 to the lower heavy talking conductor, thereby transmitting the usual busy tone back to the calling substation to inform the calling subscriber that the called line is for the time being inaccessible. Upon hearing this busy tone, the calling subscriber is expected to hang up his receiver, whereupon the connection is released.

It will now be assumed that the called line is idle when called. In this case, busy relay 106 is not energized when the wipers come to rest upon the bank contacts of the called line and relay 107, upon deenergizing at the end of the rotary movement, closes at armature 138 a circuit for the upper winding of switching relay 104 as follows: from ground by way of the grounded release trunk conductor 46, armature 135 and its resting contact, upper winding of switching relay 108, resting contact and armature 132, resting contact and armature 138, test wiper 147, switching relay 149 to the called line switch LS, and stepping magnet 150 to bat tery. Switching relay 149 energizes right away over this circuit but switching relay 108 of the connector G is slightly retarded owing to the presence of the copper collar on the upper end of its core. Switching relay 149, however, does not pull up completely owing to the usual mechanical inter-locking device (not shown) between its armature proper and that of the associated line relay, and, while all norm-ally closed contacts of the relay are opened, the switch wipers are not connected up.-

In the connector C, switching relay 108, upon energizing. shortly after theenergiza tion of switching. relay 149 of the line switch LS, disconnects busy relay 106 at armature 143 so as to prevent its energization when series relay 107 energizes subsequently, as will be pointed out later; at armature 142 removes ground from armature 139 of relay 107 and places ground on test wiper 147 independent of the upper winding of switching relay 108 at armature 142; closes a locking circuit for its lower winding at armature 144; and at armature 141 connects vertical magnet 111 to the operating circuit again, at the same time disconnecting rotary magnet 112. Rotary magnet 112 is disconnected at this time so as to prevent a further rotation of the switch wipers in case the calling subscriber again turns his calling device, and vertical magnet 111 is reconnected in order to provide a continuous circuit for release relay 103 and in order to provide a circuit for subsequently energizing relay 107, as will hereinafter appear. As a further result of the energization of switching relay 108, it connects up the line wipers 146 and 148 at armatures 140 and 145, whereupon ringing current from the common generator lead 113 is projected out over the lower conductor of the called line to ring the bridge bell at the called substation and returns by way of the upper conductor of the called line to battery through the upper winding of ring cut-off relay 105. Relay 105 is not energized by the ringing current passing through its upper winding, owing to the retarding effect of a copper collar on the upper end of the core. The small condenser 152 permits enough of the returning ringing current to pass back to the upper heavy talking conductor to enable the calling subscriber to hear a ringing tone which informs him that the called subscriber is being signalled.

When the called subscriber responds to the ringing of his bell by removing his receiver, a direct current bridge is placed across the conductors of his line, whereupon ring cut-ofl' relay 105 energizes over the calling line (the common generator conductor 113 being connected to ground through the generator winding) and closes a locking circuit for its lower winding at armature 133; disconnects the grounded test wiper 147 from the upper winding of switching relay 108 and connects it to the resting contact and armature 135 to release trunk conductor 46 so as to remove the test winding of relay 108 from the circuit over which ground is supplied to the release trunk conductor 46 'when the called man hangs up last. At armatures 131 and 134 relay 105 disconnects Wipers 146 and 148 from its own upper winding and from the common ringing lead and connects them instead to the portion of the talking circuit extending back to the talki'ng condensers and to the windings of back bridge relay 101. When this occurs, relay 101 energizes over the called line; opens a further point in the circuit of release magnet 109 at armature 124; and at armature 121 connects ground to the local locking conductor 115 so as to maintain this conductor grounded and relays 105 and 108 energized after release relay 103 has deenergized in case the calling subscriber hangs uphis receiver before the called subscriber replaces his receiver. As a further result of the energization of back bridge relay 101, it reverses the connection between conductors 45 and 47 and line relay 102 at armatures 122 and 123, thereby reversing the current How in the calling line. This reversal ofcurrent flow has no particular utility in this case but is made use of in certain cases for operating message registers and the like.

The calling and called subscribers may now converse with each other in the. usual manner, and, when the conversation is completed, the two subscribers replace their receivers. In order to bring out certain operations of the connector, it will be assumed first that the calling subscriber replaces his receiver but that the called subscriber leaves his.- receiver off the hook for the time being. In this case, when the receiver is replaced at substation A, line relay 102 deenergizes and places series relay 107 in multiple with release relay 103 at the normally closed contacts controlled by armature 125, whereupon vertical magnet 111 which has been connected to the operating circuit at armature 151 of relay 108 energizes in series with relay 107, but, the wipers of the switch are not moved, owing to the fact that the usual stationary dog of the switch mechanism prevents the shaft from being vertically raised after it has once been rotated, and it will be appreciated that this operation of vertical magnet 1'11 ismerely incidental at this time. Relay 107, upon energizing, disconnects the grounded test wiper 147 from release trunk conductor 46 at armature 138, and at armature 139 attempts to place ground on release trunk conductor 46 but is unable to do so on account of the fact that ground is disconnected from armature 139 at armature 142 of relay 108. I a

After the interval for which it is adjusted, release relay 103 deenergizes suificiently to permit its armature to be retracted owing tothe fact that it is shunted by the low wound series relay 107. At armature 126, relay 103 removes ground from the local locking conductor 115, leaving conductor 115 grounded at armature 121, and at armature 127 re.

moves ground from release trunk conductor 46, whereupon switching relay 25 of the selector S and switching relay 5 of the line switch LS deenergized, resulting in the breaking down of the connection up to andas.

far as the connector C. As a further result of the deenergization of release relay 103, it opens the operating circuit at armature 128 and attempts to close the release magnet circuit but is prevented from doing so owing to the fact that armature 124 of back bridge,

' 138 and through armature 132 and its working contact and the resting contact and armature 135, thereby guarding the connector C against seizure at this time.

The circuits remain in this condition until the subscriber at substation B replaces his receiver, and, as a matter of review, it may :be pointed out that the reason for holding the connector 0 operated at this time is to hold groundon the test contact ofthecall'ed' line to maintain switching relay 149 energized so as to prevent the associated line relay from operating to cause the line switch LS to hunt for and seize an idle first selector needlessly.

When the subscriber at substation B finally replaces his receiver, back bridge relay 101 deenergizes and closes a circuit for release magnet 109 at armature 124 astollows: from ground by way of the low wound series relay 107, normally closed contacts controlled by armature 125, armature 128 and its resting contact, armature 124 and its resti-ngconta-ct, oflf normal contact 110, and release magnet 109 to battery. Responsive to the closure of this circuit, series relay 107 energizes and removes ground from release trunk conductor 46 at armature 138, and at armature 139 prepares a circuit for grounding it again.

As a further result of the: deenergization of relay 101, it removes ground from locking conductor- 115 at armature 121, whereupon relays; 1:08 and 105 deenergize. Relay 108, in addition to disconnecting the line wipers at armatures 140 and 145, disconnects ground from test wiper 147 zit-armature 142, (permitting relay 149 of the line switch LS to deenergize) and replaces ground on release trunk conductor 46 through armature 139 and its working contact, thereby guarding the switch from seizure during the releasing operation.

Release magnet 109 energizes over the above traced circuit, including seriesrelay 107, and restores the shaft and wipers of the connector C to normal position in the usual manner, whereupon its circuit is opened at off normal contacts 110. When this occurs, release magnet 109 deenergizes and series relay 107 deenergizes shortly thereafter and removes ground from release trunk conductor 46 and armature 139, thereby permitting the switch to be seized again.

The operation of the connector C, when the called subscriber hangs up first or at about the same time that the calling subscriber hangs up, will now be explained. Assuming that the connection previously described is set up; that both subscribers have their receivers oif; and that the subscriber at substation B replaces his receiver, baclr bridge relay 101 deenergizes and reverses the direction of current flow in the calling loop back to normal, at the same time preparing a circuit for release magnet 110 at armature 124. The circuits remain in this condition until the subscriber at substation A replaces his receiver.

When the receiver is replaced at substation A, line relay 102 deenergizes and closes the circuit previously described, which includes series relay 107 and vertical magnet 111. Series relay 107 energizes and prepares at armature 139 a circuit for grounding release trunk conductor 46 during the releasing operation. After an interval, release relay 103 deenergizes and transfers the operating circuit from vertical magnet 111 to release magnet 109 at armature 128, at the same time removing ground from the local locking conductor 115 and from release trunk conductor 46 at armatures 126 and 127, respectively. Responsive to the removal of the ground potential from release trunk conductor 46, switching relay of the selector S and switching relay 5 of the line switch LS deenergize with results to be explained hereinafter.

In the connector C, responsive to the removal of ground from the local locking conductor 115, switching relay 108 and ring cutofi relay 105 deenergize and switching relay 108 in addition to disconnecting the line wipers, replaces ground on release trunk conductor 46 at armature 142 to maintain the switch guarded during the releasing operation. As a further result of the deenergization of relay 103, it shifts the locking circuit from vertical magnet 111 to release magnet 109, whereupon release magnet 109 energizes in series with relay 107 and the switch. is restored to normal position in the usual manner. The circuit of release magnet 109 and series relay 107 is opened at off normal conrelay 23, normally closed contacts controlled,

by armature 32, armature 40 and its resting contact, armature 34 and its resting contact, off normal contacts 28, and release magnet 27 to battery. Release magnet 27 and series relay 23 energize in series over this circuit and the latter closes at armature a circuit through interrupter contacts 30 and off nor mal contacts 31 for stepping relay 24. Relay 24 thereupon energizes and places ground on release trunk conductor 17 at armature 36,

thereby guarding the switch against seizure during the releasing operation. Responsive to the energization of release magnet 27, the switch is restored to normal position in the usual manner, whereupon the circuit of rev lease magnet 27 and series relay 23 is opened at off normal contacts 28 and the circuit of stepping relay 24 is opened at of? normal contacts 31, whereupon relay 24 falls back and ungrounds conductor 17 at armature 36. Release magnet 27 deenergizes upon the opening of contacts 28 and relay 23 deenergizes shortly thereafter.

In the line switch LS, the deenergization of switching relay 5 restores conditions at the line switch to normal. The entire apparatus used in setting up the previously described connection is now released and is ready to be used in another call.

Certain points in the operation of the selector S and the connector C not particularly well brought out in the preceding description will now be taken up. Considering first the selector S, it may be pointed out that, as regards the replacing of the ground potential upon release trunk conductor 17, after it is initially removed by the connector switch, in order to maintain the release trunk conductor grounded during the release of the switch, it will be at once apparent that two relays, namely, relays 23 and 24, must pull up one after the other after switching relay 25 has deenergized and closed the release circuit at armature before the ground is re-applied. The time taken for these three relays to operate one after the other is ample to permit switching relay 5 of the line switch LS to deenergize and free the line switch LS from the connection before the ground potential is re-applied. It can be seen that the same thing would be true if two or three selectors were included in the connection between the line switch LS and the selector S.

Another point in connection with the selector S is that, while the resistance associated with relay 23 and shunted around the winding thereof is provided primarily to aid the copper sleeve around the core of the relay to make the relay slow acting, this resistance has the further ellect of preventing sparking at armature 34 and its working contact, and at the oil normal contacts 28 when the circuit of series relay 23 and release magnet 27 is opened, a resistance being shunted around release magnet 27 to prevent the same from sparking, and a condenser being associated with vertical magnet 26 to prevent it from sparking.

Considering now the connector C, it will be at once apparent that a simple arrangement is provided for slowing up the reapplication of the guarding ground potential to the release trunk conductor 46 upon the release of the connector. Considering first the casein which the calling subscriber hangs up his receiver and leaves the connector C held up because the called subscriber leaves his receiver oii the hook, it has been pointed out hereinbefore that the ground potential is momentarily removed from release trunk conductor 46 when the calling subscriber hangs up to permit the line switch LS and the selector S to release, after which the ground potential is re-applied to release trunk conductor 46 to hold connector C guarded against release. Now, it will be appreciated that, under this condition, it is not necessary to again remove the ground potential from release trunk conductor 46 before the connector C is finally restored to normal. However, as pointed out hereinbefore, the ground potential is removed from release trunk conductor 46 upon the energization of series relay 107 when the release magnet circuit is closed at armature 124 when back bridge relay 101 falls back. It will be recalled also that at the same time that release magnet circuit is closed, the circuit of relay 108 is opened at armature 121 and that relay 108, upon deenergizing, replaces'the ground potential on release trunk conductor 46 at armature 142 and through armature 139 and its working contact. Although relay 108 has a copper collar on its armature end, the number and adjustment of its spring is such that it is only Very slightly slow in falling back after its circuit is opened and the ground potential is re-applied to. the release trunk conductor 46 very shortly after it is removed at armature 138 of rela 107.

Considering now t 1e release of the connector C when the called subscriberhangs up first, it will be recalled that series relay 107 is energized just as soon as linerelay 102 falls back and that it prepares at armature 139 a circuit for re-applying the ground potential to conductor 46 after it is removed and that the ground. potential is removed from conductor 46' at armature 127 when relay 103 falls back. It will be recalled also that relay 103 opens the circuit of relay 108 at armature 126 at the same time that it removes ground from conductor 46. Accordingly, the ground potential remains off the conductor 46 during the time required for the slightly slow-to-fall back relay 108 to fall back after its circuit is opened, whereupon the ground potential is re-applied at armature 142 and its resting contact and remains on conductor 46 until relay 107 deenergizes, as it does responsive to the opening of the release magnet circuit at oil normal contacts 110.

The novel points contained in the selector S, Fig. 3, over and above those contained in the selector S, Fig. 1, will now be discussed. It will be noted that the principal; difference between these two circuits is in the position of the series relay. The series relay 23 0f the selector S is connected between the resting contact of the spring controlled by the armature of the line relay and ground, and the series relay of the selector S is connected instead between the armature of the release relay corresponding to armature 34 of release relay 22 of the selector S and the resting contact of the armature of the switching relay which corresponds to the resting contact of armature 40 of switching relay 25. The reason for this change in the location of the series relay is to permit the series relay to be short circuited upon the energization of the line relay oi the selector S instead of being merely disconnected as: is the case of relay 23 of the selector S. Since the series relay of the selector S is short circuited upon eachforward stroke or the associated line relay, it is not necessary to provide this relay with a copper sleeve, as is the case of series relay 23, thereby cheapening the construction of the switch. Another difference between the two circuits is that, Whereas test wviper 43 of the selector 8. is disconnected at wipers of the selector become stuck mechanically on the contacts of a particular trunk, the test conductor thereof is grounded to prevent the seizure of that trunk during this time. This arrangement may prove desirable in a newly installed exchange Where there is a likelihood that some of the bank contacts may be out of alignment due to the undiscovered roughtreatment they might have received during shipment.

Referring now to Fig. 4, it is at once apparent. that the selector S is: similar to the selector S. 'In fact, the only difierence between-the two is that the .armature of the line relay connects to the associated vertical magnet as shown in Fig. 3 instead of to the rotary magnet through normally closed contacts on the stepping relay, as shown in Fig. 1. Accordingly, the selector S operates like the selector S except that the battery supply circuit for the release relay includes the vertical magnet in all cases, and there is, accordingly, no chance for the vertical and rotary magnets to be connected in multiple with each other, and any tendency to sparking that may be present at armature 37 and its resting contact of the selector S is eliminated.

What is claimed is:

1. In an automatic switch, a line relay, a release relay, a switching relay, and an operating magnet, means for seizing said switch and for energizing the line relay, contacts on the line relay for closing an initial energizing circuit for said release relay, a self-locking circuit for said release relay including said operating magnet, other contacts on said line relay for shunting said release relay to operate said operating magnet when the line relay falls back, means for subsequently energizing said switching relay to disconnect the line relay, and contacts on said switching .relay outside said initial energizing circuit for opening said locking circuit.

2. In a telephone system, an automatic switch having an operating magnet and a release magnet, means for energizing said operating magnet to operate said switch, means for subsequently energizing sa1d release magnet to restore said switch to its normal condition, and a relay energized in series with said release magnet to guard said switch from seizure during the releasing operation.

3. In an automatic switch, a stepping mag net, a slow acting change-over relay, a release magnet, means for operating said stepping magnet in series with said change-over relay to bring said switch in a desired position, means for subsequently operating said release magnet in series with said change-over relay to restore said switch to its normal position, and means controlled by said contacts on said line relay for connecting said change-over relay in parallel with said release relay to actuate said magnet.

6. In an automatic switch, an operating magnet, a high resistance release relay energized in series with said operating magnet, said magnet being unresponsive, a low resistance change-over relay, a line relay, and contacts on said line relay for connecting said change-over relay in parallel with said release relay to actuate said magnet, said release relay remaining in operated position in case said contacts are closed only momentarily and deenergizing because of the shunt circuit through said change-over relay in case said contacts are closed for a longer interval.

7. In an automatic switch, a line relay, an operating magnet, a release relay connected in series with said magnet when the line relay is energized, a locking circuit for said release relay also including said magnet, and a change-over relay connected to said locking circuit in parallel with said release relay when the line relay is deenergized.

8. In an automatic switch, an operating,

magnet, a line relay, a release relay energized responsive to the energization of said line relay, a locking circuit for said release relay including said operating magnet, and a change-over relay connected in series with said magnet and in parallel with said release relay when said line relay is deenergized.

9. In an automatic switch, two operating magnets and a release magnet, a change-over relay for initiating the operation of the second operating magnet after the first has operated, a circuit for energizing said relay in series with said first operating magnet, a second circuit for energizing said relay in series with said release magnet, a second relay controlling the operation of said second operating magnet after its operation has started, and a circuit controlled jointly by said relays for rendering said switch busy.

10. In an automatic switch, an operating magnet, a release magnet, a relay energized in series with the operating magnet while the switch is being set and energized in series with said release magnet while the switch is being restored to normal, a test wiper in said switch connected to the battery while the switch is in operated position, and contacts on said relay for disconnecting said test wiper from said battery. I

11. In an automatic switch, an operating magnet, and release and change-over relays connected in parallel with each other and in series with said magnet while the same is being actuated to set the switch.

12. In an automatic switch, a line relay, a

a switch, means said operating magneflmeans for deenergizing ,said line relay intermittently to operate said operating magnetby shunting said release relay, a switchin relay energized at the end of the operation oF said switch, and means controlled by said switching relay for openthe locking circuit of said release relay W ile'leavlng 1ts GIIGIglZlII circuit intact.

.13. In an automatic SWltIl, in which the release relay is maintained energized in series with the operating magnet circuit and in which the im ulse relay operates the operating magnet shunting the release relay, means operative at the end of the operation of said switch for stopping the current flow through the operating magnet, while permitting current to flow throu h the release relay.

14, In an automatic switch, a release relay,

a circuit for said relay having two branches,

one branch including an operating magnet of said switch, means for operating said magnet by momentarily shunt ng said relay, and

'ineans for opening the operating magnet. branch to prevent further operation of said magnet While maintaining the other branch closed. v p p :15. In a telephone system, an automatic or operating said switch in the course of the setting up of a telephone connection, a releasemagnet circuit in said switch, means for subsequently closing said release-magnet circuit, and means responsive to the closure of such circuit for restoring said [switch to its normal position and for guarding said switch from seizure during the restorin operation. H

16. n a telephone system,an automatic switch having an operating ma net, a release magnet, and a release-guard re ay, means for energizin said operating magnet to operate said 'switc means for subsequently energizing said release magnet to restore said switch to its normal position, means for energizing said relay during the restoring operation, and means cont-rolled by said relaywhen energ ized for guarding said switch against seizure.

17, In an automatic switch, a stepping magnet, a slow acting change-over relay, a release magnet, means for operating said stepping magnet to bring said switch in a desired posiond operating magnet after the first has operated, circuit arrangements for energizingsaid 'inaagdg relay while the first operating magnet is being operated and for energizing said relay wh le said release magnet is being opera'ted,'a second relay controlling the operation of said second operating magnet after its operation has been started, and a circuitcontrolled jointly by said relays for rendering said switch busy.

19. In an automatic switch, an operating magnet, a release magnet, a relay energized while the switch is being set by ,said operating magnet and energized while said switch is being restored to normal by said release magnet, a test wiper in said switchconnected to battery while the switch is in operated position, and contacts on said rela for disconnecting said test wiper from sai battery.

20. In an automatic switch, an operating stepping magnet, a release relay and a control relay connected in parallel with one another and in series with saidmagnet, said magnet being inoperative when connected in series with one of said two relays :alone and operative when connected in series with the other one of said two relays alone, and means for repeatedly disconnecting and reconnecting said last mentioned one relay in said parallel circuit whereby said'magnet is repeatedly operated.

21. In an automatic switch, an operating. stepping magnet, a high resistance relay connected in series therewith, a low resistance relay, means for periodically connecting and disconnecting said low resistance relay in parallel with high resistance relay, said magnet being inoperative 'in'said first mentioned circuit and operative in said second mentioned circuit. 4 22. In combination, a line'relay, a release relay, a third relay, on operating magnet,; means controlled by the line relay for estab- "lishing a series circuit for said first mentioned relay and said magnet, said magnet being inoperative in said circuit and said relay being operative in said circuit, means controlled by the line-relay for connecting said third relay in parallel with first relay in said circuit, said magnet beingoperative in said last mentioned circuit. 1

23. In an automatic switch, a line relay,ae

release relay, a third relay, an armature spring on said line relay having a normal position and an operated position, an initial operating circuit for said release relay closed tions, means'controlled'by the release relay for establishin'ga locking circuit for itself, and means controlled bysaid armature spring in its other position for connecting said third relay in parallel with "said release relay;

24. In a telephone system, an automatic switch including a'line relayfa pair ofcontrol relays, and an operating'mag'net, means controlled by the line relay forestabiishing a circuit including said control relays in parj by saidarmaturespringin' one of sai-d posiallel with one another and in series with said magnet, means controlled by the energization and deenergization of said line relay for alternately disconnecting one of said relays from said parallel circuit leaving the magnet and the other of said relays connected in series, the windings of said control relays having resistances so proportioned that said magnet operates when both of said relays are connected in parallel in said first mentioned circuit, and releases its armature when said one relay is disconnected from said circuit.

25. In a telephone system, an automatic switch having a line relay energized in a closed line circuit, said switch having also a release relay and a magnet connected in series, said release relay having sufficient resistance to prevent the operation of said magnet, means for deenergizing said line relay momentarily a desired number of times, contacts controlled by said line relay for connecting a low resistance change-over relay in parallel with said release relay upon each deenergization of said line relay whereby said magnet is caused to operate, a secondary magnet, and a circuit for the secondary magnet controlled by the change-over relay.

In witness whereof, I hereunto sub-scribe my name this 15th day of October, A. D.

RUDOLPH F. STEHLIK. 

